1. Field of the Invention
The present invention relates to an optical add/drop device, and more particularly to an optical add/drop device suitable for wavelength division multiplexing (WDM) communication network.
2. Description of the Related Art
With the recent extension of data communications primarily including Internet, a rapid increase in traffic has started and it is expected that the trend of such a traffic increase will further continue in the future. In response to this traffic increase, a network having a hitherto unattained large capacity is required, and the construction of an optical communication network is proceeding to meet this requirement.
It is desired to use a transmission device adapted to a WDM communication network. For example, it is required to introduce a WDM-adapted device capable of processing a large-capacity signal into a node.
On the other hand, a ring topology relatively easy to control and usable on the scale of a small-sized switch is now introduced in small- to medium-scale networks. In the future, it will be tried to expand such a ring topology up to the form of a chain and thereby to cover a wide area. In this respect, the improvement in an optical add/drop device used as a node is desired in order to improve the reliability of a network and effect an efficient and economical operation of the network.
In a conventional optical add/drop device known in the art, an optical demultiplexer and an optical multiplexer are used to establish wavelength channels in each line, and a switch unit is used per wavelength channel to perform switching of optical paths. For example, the switch unit is configured by arranging a plurality of 2xc3x972 switch elements in the form of a matrix.
Each 2xc3x972 switch element can switch between a bar state and a cross state. Examples of such a 2xc3x972 switch element include an optical waveguide type switch element and a reflection type switch element such as a mirror using MEMS (Micro Electro Mechanical System).
In considering optical path switching upon failure restoration in a ring network or the like, there is a problem that the number of switch elements in an optical add/drop device increases to cause a complex configuration of the device. Furthermore, there are various modes of responding to the optical path switching upon failure restoration, and it is accordingly desired to prepare an optical add/drop device capable of supporting these various modes.
It is therefore an object of the present invention to provide an optical add/drop device which can easily perform failure restoration with a simple configuration.
In accordance with an aspect of the present invention, there is provided an optical add/drop device applicable to an optical fiber network. This device comprises a plurality of 2xc3x972 switch elements provided on crosspoints arranged in the form of a matrix, each of said switch elements switching between a bar state and a cross state; input/output ports provided on the rows of said matrix and connected to said optical fiber network; and add/drop ports provided on the columns of said matrix.
With this configuration, in the case of applying this optical add/drop device to a ring network, for example, failure restoration can be easily performed. Further, the configuration of the optical add/drop device can be simplified through various preferred embodiments of the present invention.
Preferably, said matrix comprises a 4xc3x974 matrix.
In this case, said add/drop ports comprise two add input ports opposed to said switch elements in the first row, the first column and in the first row, the second column; and two drop output ports opposed to said switch elements in the fourth row, the first column and in the fourth row, the second column.
Further, said optical fiber network comprises a first work line, a second work line opposite in direction of said first work line, a first protection line, and a second protection line opposite in direction to said first protection line. Said input/output ports comprise four input ports opposed to said switch elements in the first row, the first column, in the second row, the first column, in the third row, the first column, and in the fourth row, the first column, and connected to said first work line, said second work line, said first protection line, and said second protection line, respectively; and four output ports opposed to said switch elements in the first row, the fourth column, in the second row, the fourth column, in the third row, the fourth column, and in the fourth row, the fourth column, and connected to said first work line, said second work line, said first protection line, and said second protection line, respectively. All of said switch elements in the first, second, and third columns are oriented in a first direction, and all of said switch elements in the fourth column are oriented in a second direction different from said first direction.
In accordance with another aspect of the present invention, there is provided an optical add/drop device applicable to an optical fiber network for propagating WDM signal light obtained by wavelength division multiplexing a plurality of optical signals having different wavelengths. This device comprises an optical demultiplexer and an optical multiplexer for relating said optical fiber network to a plurality of wavelength channels; and a plurality of switch units provided so as to respectively correspond to said plurality of wavelength channels. Each of said switch units comprises a plurality of 2xc3x972 switch elements provided on crosspoints arranged in the form of a matrix, each of said switch elements switching between a bar state and a cross state; input/output ports provided on the rows of said matrix and connected to said optical fiber network; and add/drop ports provided on the columns of said matrix.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.